Reduced synaptophysin, syntaxin, and PSD-95 levels in Tg6799: synaptic degeneration. A, Whole-brain homogenates from 2- to 12-month-old Tg6799 and 9-month-old nontransgenic control (9C) mice were analyzed for synaptophysin by ELISA. Synaptophysin levels are expressed as the percentage of 9-month-old control whole-brain synaptophysin levels (9C is 100%). No significant gender differences were observed in Tg6799 synaptophysin levels at any given age (data not shown), so values from age-matched males and females were pooled (3 mice for each gender and age). Note the steady decline in synaptophysin levels starting at 4 months in Tg6799, eventually falling to ∼75% of control levels at 9 months. B, C, Immunoblot analysis of synaptic markers syntaxin and PSD-95 in cortex homogenates (15 mg) from Tg6799 (Tg) and nontransgenic (wild type, WT) mice (3, 9, and 12 months old). Equal loading was determined by ponceau red staining of the blots (data not shown). Immunoblot signals were captured using a PhosphorImager (B), quantified, and expressed as percentage of age-matched control (C). Note that synaptic markers are significantly reduced by 9 months of age in Tg6799, indicating neurodegeneration. Error bars represent SEM.